This invention relates to viscosity index improver oil compositions, exhibiting reduced haze, and to a process for preparing such compositions.
An important property of a lubricating composition is the rate at which its viscosity changes as a function of temperature. One of the major requirements of lubricating oils is a satisfactory viscosity-temperature characteristic so that the oils will not lose their fluidity but will show an equally good performance within a relatively wide temperature range to which they may be exposed in service. The relationship between viscosity and temperature is commonly expressed as the viscosity index (VI). It has been common practice to introduce long chain hydrocarbon compounds to improve viscosity index of lubricant compositions. It is known to utilize ethylene-alpha olefin copolymers such as ethylene-propylene copolymers as viscosity index improvers. Their structure can be modified to produce multifunctional additives which not only improve the VI, but also impart other properties to oil such as dispersance. Dispersant OCP (DOCP) VI improvers are frequently used in place of simple OCP in motor oil as they dramatically decrease the amount of succinimide dispersant required to maintain a desired performance level. Such VI improvers are based on OCP containing very small amounts (typically about one wt %) of pendant functionality of polar functionality such as an imide or heterocyclic amine, for example pyrrolidone or piperazine.
It is often found during the preparation processing, and/or storage of these various oil soluble hydrocarbon polymers that a haze develops in their oil concentrates. It is believed that the haze in OCP VII is due to presence of a wide variety of catalysts, metal acid salts or copolymers, etc., which are used in Ziegler-Natta copolymerization. In DOCP VI improvers there is an additional source of haze: homopolymer formed from the functional monomer being grafted onto OCP. Thus, for example a typical haze producing agent in DOCP containing groups derived from N-vinylpyrrolidone is polyvinylpyrrolidone.
It has been now discovered that the haze of such VI improver can be reduced or substantially eliminated by the addition thereto or treatment thereof with a small amount of water or diol.
Thus, it is an object of this invention to provide a method for making a clear, high-performing dispersant VI improver.